I finished building my FT-5 R2 and just did my second test cube (first was with PLA) using Taulman 'Bridge' nylon, which the manufacturer says should run at 250 C. I've been assured in another thread that anything over 240 C would destroy the heat break in the hot end, but I was willing to test to destruction, knowing that I'd need an upgrade anyhow, and the stock setup would eventually be shelved no matter what.

I'm using the latest versions of Repetier and Marlin firmware.

First thing I discovered is that the moment the hot end hits 250, I get a MAXTEMP error and the print run is automatically killed. Due to thermostatic fluctuations over and under the target temp, I was only able to preheat to a target temp of 244 C. Overshooting from a target of 245 C got me a MAXTEMP error about half the time.

Coaxed to print at 244 C, I got decent results, sort of. I discovered that whilst set to run at that temp, Repetier was working in the background to default back to the temp settings for PLA. I caught it and reset the hot end temp, but not before I hit a severe failure to adhere on one of the early layers.

Tried to run the temperature settings from the onboard screen instead, but it won't accept any temp for the hot end any higher than 235 C. I have the impression that I have to invade the code with a modification to get the temp I want/need.

Q1: I have not had any extruder problems so far, so I'm tempted to get a hot end that's compatible with the stock extruder. What choices do I have for a compatible high-temp hot end?

Q2: Would it be a better option to get a complete extruder plus hot end? If so, is there an extruder that's compatible with the stock mounting brackets? Or will I have to get new mounting brackets, too? If I do, where do I go for the brackets?

Q3: Assuming that I get whatever hardware I need to print high-temp filament, how can I persuade the FT-5 R2 that it's OK to run hotter? It's being quite stubborn on this point.

It looks like the MicroSwiss MK8 upgrade would be what you are trying to find. It would be a direct replacement and compatible with the stock cold end block and heater block. I haven't tested it so I cannot say how well or not it performs, but it looks like quality gear. I personally use an E3Dv6 solution.